1. Field of the Invention
This invention is in the file of Schottky gate field effect transistors with the inclusion of a space charge zone in proximity to the interface between the silicon transistor body and the substrate in combination with a thin active layer located between such space charge zone and the gate electrode of the transistor.
2. Description of the Prior Art
Schottky gate field effect transistors also known as MESFET are described in the publications of Drangeid and Sommerhalder (IBM Journal Res. Develop., March 1970, pages 82 to 94) and Mohr (IBM Journal Res. Develop., March 1970, pages 142 to 147). The first publication states that power amplification is possible even in the gigahertz range with such a transistor. For such transistors consisting of silicon, a limiting value of approximately 12 gigahertz was established, and in the case of such transistors constructed from gallium arsenide, 30 gigahertz was considered to be the highest oscillation frequency. In addition to good high frequency properties, a further advantage of the MESFETs is that they can be produced relatively simply with easily reproducible, low threshold voltages.
For integrated circuits, silicon is used as the transistor material. However, circuit elements on a silicon base and circuit elements on a gallium arsenide base cannot be positioned together on a common substrate in a simple fashion and thus the use of MESFETs consisting of gallium arsenide is limited.
The second-named publication discloses the prior art for MESFETs on a silicon base. Previously, silicon having a high electrical resistance had been used as the substrate for the MESFET. On pages 142 and 143 of this publication, it is stated that this type of silicon as a substrate merely represents a compromise because its insulating properties are not ideal. Accordingly, such transistors have been constructed in which the active region is isolated from the exterior, for example, by a ring-shaped source electrode. This closed arrangement, however, occupies a significant amount of space. A further difficulty arises from the fact that the electric properties of the silicon substrate can change during the production of the integrated circuits. Nevertheless, as stated in this publication, silicon MESFETs on silicon substrates are preferred to silicon MESFETs on sapphire substrates and to other heterogeneous silicon MESFETs. The reason for this is that thin silicon layers having a thickness of 0.2 micron or less such as have previously been used for MESFETs cannot be produced with sufficiently high crystallographic and electrical quality on other than silicon substrates.